Abstract : This paper focuses on students' construction of meaning and teacher control of learning in computer-based learning environments. The new complexity brought about by modern learning environments is discussed and illustrated from the point of view of learning and of teaching. The analysis presented is based on data gathered in the context of a distance tutoring scenario using the experimental platform Telecabri—Telecabri is a research action of the project Cabri-g6ometre. The conclusion introduces two issues for further discussion: the type of knowledge teachers should have of the mathematics underlying the software they use, and the nature of the knowledge constructed by students in the course of their interactions with a learning environment.